Make QMap (and other containers?) more SL compliant

I heard that Qt-6 is already more or less on rails.  Maybe is it time to make QMap and other QContainers more SL compilant?

QMap is defined as

template <typname Key, typename Value>class QMap

but std::map is defined as

template <typname Key, typename Value, typename Comp = less, typename Alloc=allocator<pair<Key, Value>>class map

Even if the last template parameter has maybe none interes, i think (for five years, see QTBUG-31927) that it should be interesting to add the third template parameter (Comp for "comparator") to QMap.

In some occason, we can effectively want to get data sorted in an other way than from lesser to greater.

Bug QTBUG-31927 was rejected because it should break the binary compability, and I did respect that.

But, since contributor are starting to work on the master 6 version, it is maybe time to do this, it could make QMap more compliant with some algorithms we could use.

NOTA: there are maybe other Qcontainers whose could integrate similare evolution